No abstract

A paragenetic sequence of the common mineral constituents of the uraniferous vein deposits of the Fay Mine and Bolger open pit of Eldorado Nuclear Ltd., in northwestern Saskatchewan, is presented.Pitchblende associated with hematite, pyrite, chalcopyrite, bornite, galena, and clausthalite in quartz ± calcite ± dolomite gangues is found in veins cutting folded Tazin metamorphics, adjacent to the St. Louis Fault. Fluid inclusion studies reveal a cooling sequence from the initial phase of mineralization at 440 ± 30 °C down to the final stages at around 80 ± 10 °C. Stable isotope studies, augmented by petrographic data, serve to distinguish at least five generations of carbonate in the ore veins. Early generations of dolomite have apparently not undergone any significant recrystallization or isotopic readjustment and exhibit original restricted δ18O (SMOW) values of 9.5 to 11.0‰ and δ13C (PDB) values of −0.60 to 0.55‰. Isotopic evolution via equilibration with wall rocks has resulted in the deposition of late-stage calcites characterized by δ18O (SMOW) values of + 13.2 to + 14.5% and δ13C (PDB) values of −15.9 to −16.8‰. The strong decrease in δ13C may possibly be explained by a decrease in the amount of CH4 present in the system. It is felt that the deposits were generated by metamorphic hydrothermal fluids with initial δ18O (SMOW) values of + 6 to + 8‰, which during cooling underwent isotopic exchange with the host metamorphic rocks and became depleted in 18O. The final stages of mineralization were possibly effected by some influx of isotopically lighter surface waters into an otherwise essentially 'closed' system. Present day waters from the Fay Mine have δ18O (SMOW) values of −16.0 to −16.2‰ and could represent products of a continuing evolution of the hydrothermal fluids.

Whole-rock Rb–Sr studies of metamorphic rocks and associated discordant pegmatites from the Fay Mine, NW Saskatchewan, confirm that the gneisses of the Beaverlodge area have a minimum age of 2100 m.y., while the pegmatites are 1975 ± 20 m.y. old. The amphibolite facies grade metamorphic suite reveals that a significant degree of 'open system' behavior (with respect to Rb and Sr) accompanied intense kinematic metamorphism, mineralization, and partial retrogression into the greenschist facies. In contrast, the pegmatites which exhibit minimal cataclasis, have apparently remained 'closed systems'.

No abstract

The Fay Mine uranium deposit is composed of veins parallel to the foliation of the paragneisses and paraschists of the Fay Mine Complex, which in turn overlies the Donaldson Lake Gneiss and Foot Bay Gneiss, within the Tazin Group of the Beaverlodge District, northern Saskatchewan. A computer oriented study of 5500 strike-dip measurements of planar features within the Fay Mine reveals that the lowest member of the metamorphic sequence, the Foot Bay Gneiss, is unique in that it exhibits Kenoran (?) structures associated with F1, NW-SE or N-S trending folds. Subsequent to the Kenoran (?) folding, an Aphebian (?) sequence of sediments and volcanics, now represented by the Donaldson Lake Gneiss and the Fay Mine Complex, was deposited. NE-SW trending, Hudsonian, F2 folds then developed and extensive cataclasis was effected. The F2 structures also affected the uppermost, taphrogeosynclinal Martin Formation sediments and volcanics. The major faults of the district are thought to have been initiated either as F2-shear joints or F2-tension fractures and have undergone multiple movement over a long period of time. The pitchblende ± quartz ± carbonates ± hematite ± chlorite veins, classified as 'mobilized stratabound deposits', occur parallel to S2 foliation planes in the crests, troughs, or limbs of F2 folds, wherever minimal plunge is observed. Such deposits may have been generated during regional metamorphism by mobilization of uranium-rich fractions from the originally uraniferous Aphebian precursors of the Fay Mine Complex. Later movement of such major structures as the St. Louis Fault has apparently caused only local deformation and brecciation of the uraniferous veins and has caused no more than limited recrystallization.